Optical coherence tomography is a non-invasive and non-contact imaging modality that enables two-dimensional cross-sectional and three-dimensional volumetric imaging of tissue architecture.

It has evolved over the past decade as one of the most important ancillary tests in ophthalmic practice. It is a noninvasive imaging technique and provides high resolution, cross-sectional images of the retina, the retinal nerve fiber layer and the optic nerve head. With axial resolution in the 5-7 μm range, it provides close to an in-vivo 'optical biopsy' of the retina. Optical coherence tomography employs light from a broadband light source, which is divided into a reference and a sample beam, to obtain a reflectivity versus depth profile of the retina. The light waves that are back scattered from the retina, interfere with the reference beam, and this interference pattern is used to measure the light echoes versus the depth profile of the tissue in vivo.

Recently, a new type of optical coherence tomography instrument, called a swept source optical coherence tomography, was introduced. The Swept source optical coherence tomography uses a tunable laser (swept-source) as a light source with a longer wavelength that allows the light to penetrate deeper into tissues than the conventional spectral domain optical coherence tomography instruments. This, then, enabled the imaging of the choroid.

Because choroidal abnormalities such as vascular hyperpermeability, vascular changes, loss and thinning are critical to the onset and progression of many ocular diseases, ophthalmologists and researchers are shifting their interest to the choroidal abnormalities.

Being a major vascular layer of the eye , choroid plays an important role in ocular health, and is involved in the pathogenesis of many intraocular diseases such as age-related macular degeneration , polypoidal choroidal vasculopathy , central serous chorioretinopathy and myopic macular degeneration. Accurate measurement of choroidal thickness in vivo is an essential step in monitoring disease onset and progression that lead to choroidal thinning. Based on histologic study, choroidal thickness ranges from 170 to 220 um.

These disorders show the need for understanding the choroidal structure in ocular diseases and the importance of having database of choroidal thickness.

Inclusion Criteria:

• Age from 18 years to 40 age.
• Spherical equivalent from zero to -8.
• Minimum corneal thickness from 500 to 540.
• Refractive power of cornea more than 41 diopter.
• Axial length from 22 to 26.

Exclusion Criteria:

• Corneal abnormalities such as ectasia.
• Eyes with dystrophic or degenerative diseases.
• Prior ocular surgery.
• Anterior or posterior segment inflammation.
• Glaucoma.
• Eyes with choroidal abnormalities or conditions that could affect choroidal thickness such as central serous chorioretinopathy, nevus, pregnancy, or haemangiomas.
• Patients with diabetes mellitus.
• Patients with optical media opacity that significantly disturb optical coherence tomography image acquisition.

100 case of age from 18 to 40 years old of myopic refraction from zero to -8 diopter , minimum corneal thickness from 500 to 540 micrometer , refractive power of cornea more than 41 diopter and axial length from 22 to 26 millimeter